Just weighing in with what appears to be the standard opinion, that I don't see anything particularly odd about the relationship. I've been in a number of relationships of varying lengths and wouldn't have a problem dating someone with little to no experience in that regard (though given how long it's been, I might be equally in need of "figuring things out," or in need of some mental WD-40 at the least). Age gaps don't matter so much, either, I think life experience has more to do with it. For example, while I'd not have a problem dating a 21 year old (I refuse to consider younger, you gotta be able to buy your own hooch, dammit), the likelihood of someone that young matching my level of life experience and/or maturity is pretty low, as is having anything meaningful in common.
In the end, though, as was previously said, the heart wants what it wants, and if you're really into someone, you'll find a way to work through the problems.